The invention relates to a device for adding fluid to a liquid. The term “fluid” should here be understood as a gas, a liquid or a mix of these, possibly with the addition of particles. Some particle masses may also be treated and transported as a fluid.
For some purposes there is a need for treatment of liquids, such as melted metals, by addition of a fluid. Particularly actual fluids in connection with metal melting are a gas and/or a particular material. For this purpose it is known to use a device with a rotor which is submerged in the liquid and where a fluid, that is gas and/or particles, is added through the inner part of the rotor.
Such a rotor may comprise a hollow rotational body with openings in the bottom and the side, which is mounted and driven via a shaft by a driving unit and that is arranged to be lifted out of and lowered into the liquid. When a gas reacts with a liquid, the speed of the reaction will be a function of the surface of the gas bubbles that is in inverse ratio with the diameter of the gas bubbles. That is, gas bubbles with a small diameter are desired.
Generally there is a desire for rotors in treatment of liquid, in particular treatment of melted metals, that the addition of gas or a particular material is effective. At the other side, there is also a desire not to create too much stirring or turbulence which causes a turbulent surface and whirls in the liquid and thereby causes an increased addition of undesirable gas from the environment (atmosphere).
It is previously known equipment for treatment and addition of a particular material in a liquid as mentioned above. Thus it is known from the inventors Norwegian patent 155447 a rotor for treatment and addition of material in a liquid where the rotor is constituted by a symmetric rotational hollow body, and where the material is added to the liquid via a bore in the rotor shaft and further out through a hole in the side of the hollow body together with the liquid, which due to the centripetal force is sucked in through an opening in the bottom and circulate through the body.
From the inventors own patent Norwegian patent application 19983142 it appears a solution by rotors for treatment of liquid where the efficiency when intermixing gas or particles into a liquid is close to doubled, but where the stirring is maintained unchanged related to the design shown in NO 155447. Further it is reached a solution by rotors where the use of gas/particles is less than the half.
From the Norwegian patent 307289 it is known a device for addition of a fluid to a liquid, for example of gas and/or particles to a liquid metal, with a rotor which is driven immersed in the liquid and which comprises a hollow rotational body with a first inner annular wall and at least one radial opening from a centrally, cylinder shaped hollow room with an opening facing downwards, as the rotational body is carried by a generally vertical shaft which is connected to a driving unit and which may be arranged to lift the rotational body out, respectively lower it into the liquid, where it outside the central annular wall of the rotational body is arranged an additional annular wall which forms an annular chamber, which communicates with the central chamber through the one or more radial openings.
A disadvantage of this design of the rotor is that liquid which contains bubbles or powder, and which comes out of the central chamber, comes into an annular chamber with a narrow opening and small volume for mixing the bubbles or powder into the liquid. What would have been satisfactory in a liquid with low specific weight, for example water, does not work satisfactory in liquid metal, for example aluminium.